KCNA Kubernetes Fundamentals Practice Question
You have a Deployment with image: myapp:v1. You update the image to myapp:v2 using 'kubectl set image deployment/myapp myapp=myapp:v2'. The rollout status shows 'Waiting for rollout to finish: 0 out of 3 new replicas have been updated...'. What is the most likely cause of this behavior?
⚠ Common exam trap
Many candidates assume a syntax error (Option A) or a Pod crash (Option B) when the real issue is a missing or inaccessible image, which is a common cause of stuck rollouts in Kubernetes.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The new image myapp:v2 does not exist or cannot be pulled from the registry
The rollout is stuck waiting for new replicas to become ready, which typically happens when the container image cannot be pulled. The message '0 out of 3 new replicas have been updated' indicates that the ReplicaSet is attempting to create Pods with the new image, but the Pods are failing to start. The most common cause is that the image tag 'myapp:v2' does not exist in the registry or cannot be accessed due to authentication or network issues, preventing the kubelet from pulling it.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The command syntax is incorrect; you should use 'kubectl set image deployment/myapp myapp:v2'
Why it's wrong here
The command syntax is valid: 'kubectl set image deployment/myapp myapp=myapp:v2' correctly names the container and new image, so it is not the cause. It is tempting because malformed set image commands do fail silently, and it would be correct if the container name or resource name were misspelled.
- ✗
The new Pods are crashing due to a missing command
Why it's wrong here
Crashing Pods would cause CrashLoopBackOff, but the rollout would still attempt to update replicas; however, the specific message '0 out of 3 new replicas have been updated' suggests the new Pods are not being created.
- ✗
The Deployment's update strategy is set to 'Recreate'
Why it's wrong here
Recreate terminates all existing pods before starting new ones, so the status would show old replicas dropping to zero, not three new replicas pending. It is tempting because Recreate does stall rollouts, and it would be correct if the status showed the old ReplicaSet scaling down first.
- ✓
The new image myapp:v2 does not exist or cannot be pulled from the registry
Why this is correct
New pods stay unscheduled or stuck in ImagePullBackOff when the container runtime cannot fetch myapp:v2, so no new replicas become ready and the rollout stalls at zero updated. A missing or inaccessible image tag directly explains the reported waiting status.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This KCNA practice question is part of Courseiva's free CNCF certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the KCNA exam.